If terrorism means bringing terror to a
population, it is unislamic. It is unislamic because it brings
about an extreme fear of people. To have such an intention has
nothing to do with Islam. In Islam Muslims seek to instil in
people a fear of God's anger only and NOT of people.

There are some who hate that people should
fear God's anger only. They set themselves up as enemies of God
and the Muslims. They may try to force people to fear something
else. By doing so they are themselves at least mild terrorists.
If they do so then Muslims have a duty to oppose this force -
with force if necessary and if it will be effective and decisive.
In this way only those who are themselves 'terrorist' have cause
to fear the use of force by Muslims.

It is the complete incompatibility of only
fearing God with fear of people which is referred to in verse
2:256 of the Qur'an:

Let there be no compulsion in
religion: Truth stands out Clear from Error: whoever Rejects
Evil and Believes In Allah hath grasped The Most trustworthy
Handhold that never breaks.

The ignorant or the liars may stand up
proclaiming that there is such a thing as an Islamic terrorist.
There isn't.

The Muslims don't want you to fear them.
They only hope that you will learn to devote your life to seeking
Allah's pleasure and fearing His displeasure.